LIBXO(3) FreeBSD Library Functions Manual LIBXO(3)
NAME
libxo - library for emitting text, XML, JSON, or HTML output
LIBRARY
Text, XML, JSON, and HTML Output Emission Library (libxo, -lxo)
SYNOPSIS
#include <libxo/xo.h>
DESCRIPTION
The functions defined in libxo are used to generate a choice of TEXT,
XML, JSON, or HTML output. A common set of functions are used, with
command line switches passed to the library to control the details of the
output.
Most commands emit text output aimed at humans. It is designed to be
parsed and understood by a user. Humans are gifted at extracting details
and pattern matching. Often programmers need to extract information from
this human-oriented output. Programmers use tools like grep(1), awk(1),
and regular expressions to ferret out the pieces of information they
need. Such solutions are fragile and require updates when output
contents change or evolve, requiring testing and validation.
Modern tool developers favor encoding schemes like XML and JSON, which
allow trivial parsing and extraction of data. Such formats are simple,
well understood, hierarchical, easily parsed, and often integrate easier
with common tools and environments.
In addition, modern reality means that more output ends up in web
browsers than in terminals, making HTML output valuable.
libxo allows a single set of function calls in source code to generate
traditional text output, as well as XML and JSON formatted data. HTML
can also be generated; "<div>" elements surround the traditional text
output, with attributes that detail how to render the data.
There are four encoding styles supported by libxo:
• TEXT output can be display on a terminal session, allowing
compatibility with traditional command line usage.
• XML output is suitable for tools like XPath and protocols like
NETCONF.
• JSON output can be used for RESTful APIs and integration with
languages like Javascript and Python.
• HTML can be matched with a small CSS file to permit rendering in any
HTML5 browser.
In general, XML and JSON are suitable for encoding data, while TEXT is
suited for terminal output and HTML is suited for display in a web
browser (see xohtml(1) ).
The libxo library allows an application to generate text, XML, JSON, and
HTML output using a common set of function calls. The application
decides at run time which output style should be produced. The
application calls a function xo_emit(3) to product output that is
described in a format string. A "field descriptor" tells libxo what the
field is and what it means. Each field descriptor is placed in braces
with a printf-like format string:
xo_emit(" {:lines/%7ju} {:words/%7ju} "
"{:characters/%7ju}{d:filename/%s}\n",
linect, wordct, charct, file);
Each field can have a role, with the 'value' role being the default, and
the role tells libxo how and when to render that field, as well as a
printf(3)-like format string.
Output can then be generated in various style, using the "--libxo"
option.
DEFAULT HANDLE
Handles give an abstraction for libxo that encapsulates the state of a
stream of output. Handles have the data type "xo_handle_t" and are
opaque to the caller.
The library has a default handle that is automatically initialized. By
default, this handle will send text style output to standard output. The
xo_set_style(3) and xo_set_flags(3) functions can be used to change this
behavior.
Many libxo functions take a handle as their first parameter; most that do
not use the default handle. Any function taking a handle can be passed
NULL to access the default handle.
For the typical command that is generating output on standard output,
there is no need to create an explicit handle, but they are available
when needed, e.g., for daemons that generate multiple streams of output.
FUNCTION OVERVIEW
The libxo library includes the following functions:
Function Description
xo_attr()
xo_attr_h()
xo_attr_hv() Allows the caller to emit XML attributes with the
next open element.
xo_create()
xo_create_to_file() Allow the caller to create a new handle. Note
that libxo has a default handle that allows the
caller to avoid use of an explicitly created
handle. Only callers writing to files other than
stdout would need to call xo_create().
xo_destroy() Frees any resources associated with the handle,
including the handle itself.
xo_emit()
xo_emit_h()
xo_emit_hv() Emit formatted output. The fmt string controls
the conversion of the remaining arguments into
formatted output. See xo_format(5) for details.
xo_emit_warn()
xo_emit_warnx()
xo_emit_warn_c()
xo_emit_warn_hc()
xo_emit_err()
xo_emit_errc()
xo_emit_errx() These functions are mildly compatible with their
standard libc namesakes, but use the format string
defined in xo_format(5). While there is an
increased cost for converting the strings, the
output provided can be richer and more useful.
See also xo_err(3)
xo_warn()
xo_warnx()
xo_warn_c()
xo_warn_hc()
xo_err()
xo_errc()
xo_errx()
xo_message()
xo_message_c()
xo_message_hc()
xo_message_hcv() These functions are meant to be compatible with
their standard libc namesakes.
xo_finish()
xo_finish_h() Flush output, close open construct, and complete
any pending operations.
xo_flush()
xo_flush_h() Allow the caller to flush any pending output for a
handle.
xo_no_setlocale() Direct libxo to avoid initializing the locale.
This function should be called before any other
libxo function is called.
xo_open_container()
xo_open_container_h()
xo_open_container_hd()
xo_open_container_d()
xo_close_container()
xo_close_container_h()
xo_close_container_hd()
xo_close_container_d()
Containers a singleton levels of hierarchy,
typically used to organize related content.
xo_open_list_h()
xo_open_list()
xo_open_list_hd()
xo_open_list_d()
xo_open_instance_h()
xo_open_instance()
xo_open_instance_hd()
xo_open_instance_d()
xo_close_instance_h()
xo_close_instance()
xo_close_instance_hd()
xo_close_instance_d()
xo_close_list_h()
xo_close_list()
xo_close_list_hd()
xo_close_list_d() Lists are levels of hierarchy that can appear
multiple times within the same parent. Two calls
are needed to encapsulate them, one for the list
and one for each instance of that list. Typically
xo_open_list() and xo_close_list() are called
outside a for-loop, where xo_open_instance() it
called at the top of the loop, and
xo_close_instance() is called at the bottom of the
loop.
xo_parse_args() Inspects command line arguments for directions to
libxo. This function should be called before argv
is inspected by the application.
xo_set_allocator() Instructs libxo to use an alternative memory
allocator and deallocator.
xo_set_flags()
xo_clear_flags() Change the flags set for a handle.
xo_set_info() Provides additional information about elements for
use with HTML rendering.
xo_set_options() Changes formatting options used by handle.
xo_set_style()
xo_set_style_name() Changes the output style used by a handle.
xo_set_writer() Instructs libxo to use an alternative set of low-
level output functions.
SEE ALSO
xo(1), xolint(1), xo_attr(3), xo_create(3), xo_emit(3), xo_emit_err(3),
xo_err(3), xo_finish(3), xo_flush(3), xo_no_setlocale(3),
xo_open_container(3), xo_open_list(3), xo_parse_args(3),
xo_set_allocator(3), xo_set_flags(3), xo_set_info(3), xo_set_options(3),
xo_set_style(3), xo_set_writer(3), xo_format(5)
HISTORY
The libxo library first appeared in FreeBSD 11.0.
AUTHORS
libxo was written by Phil Shafer <phil@freebsd.org>.
FreeBSD 13.1-RELEASE-p6 December 8, 2014 FreeBSD 13.1-RELEASE-p6
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